High speed instrument clutch



Nov. 1, 1967 J. T. POTTER ET AL HIGH SPEED INSTRUMENT CLUTCH Filed Feb. 9, 1965 Tlc l.

2 Sheets-Sheet 1 INVE 0R5 ATTORNEY Nov. 7, 1967 J. "r. POTTER ET HIGH SPEED INSTRUMENT CLUTCH 2 Sheets-Sheet 2 Filed Feb. 9, 1965 ATTORNEY INVENTORS United States Patent Office 3,351,166 Patented Nov. 7, 1967 3,351,166 HIGH SPEED INSTRUNENT CLUTCH John T. Potter, Plainview, and Gerald D. Cohen, Massapequa, N.Y., assignors to Potter Instrument Company, ind, llainview, N.Y., a corporation of New York Filed Feb. 9, 1965, Ser. No. 431,256 4 Claims. (C1. 19221.5)

The present invention, generally, relates to clutches having magnetic particles for engaging and disengaging the driving and driven members, and more particularly, to a magnetic particle clutch which can be cycled at a high rate to produce a high speed intermittent rotary drive.

The usual magnetic particle clutch has a rotor operating within a cylinder filled with a mixture of small iron particles and a lubricant. An electrical coil surrounds the mixture to produce a magnetic field across the rotor an cylinder when the coil is energized, so that the iron particles are attracted to one another and to the rotor and cylinder to drivingly connect them together. When the coil is deenergized, the only force restraining relative rotation between the rotor and cylinder is the viscous drag of the magnetizable mixture.

While prior art magnetic particle clutches have been successfully employed in many applications, they have several troublesome drawbacks when cycled at high rates. One drawback is excessive heating of the magnetic particles under slip conditions which may result in breakdown or degeneration of the particles. Another is the tendency for the magnetic particles to settle out of the lubricant when the clutch is at rest and to centrifuge outwardly during the operation of the clutch in a manner to pack and lock the coacting clutch surfaces together. Still another drawback is the dilficulty in maintaining the ability of the clutch to transmit torque of a substantially constant value without fading after the clutch has been in service for a period of time, or fading due to heating and other causes.

These problems are particularly troublesome in con nection with magnetic particle clutches which must be cycled at high rates to produce an intermittent drive, such as a clutch for intermittently rotating a capstan adapted to drive a magnetic tape past a reading and writing transducer at very fast start-stop rate. The prior art magnetic particle clutches have not been completely satisfactory for such use because they do not produce the required acceleration and deceleration rates for the capstan.

Accordingly, it is one object of the present invention to provide a high speed magnetic particle clutch which can be cycled at high rates to engage and disengage the driving and driven members rapidly.

It is another object of this invention to provide a high speed magnetic particle clutch of the type described above which is particularly useful for intermittently rotating a capstan for driving a magnetic tape past a magnetic tape reading and writing transducer.

It is still another object of the invention to provide a high speed magnetic particle clutch of the type described above having a carefully formulated powder-like mixture of magnetic particles and lubricant particles which is particularly suited for high speed, fast cycling intermittent drive applications.

It is yet another object of the invention to provide a high performance magnetic particle clutch having a low inertia design which minimizes response time and enables extremely high rates of acceleration and deceleration to be obtained to improve the performance of the clutch.

It is a further object of the invention to provide a magnetic particle clutch having a new and improved seal for sealing the magnetic particles in the rotor chamber.

It is a still further object of the invention to provide a magnetic particle clutch which can be magnetized and clemagnetized very quickly to engage and disengage the clutch.

It is also an object of the invention to provide a magnetic particle clutch which is simple in design, economical to manufacture and effective in use.

Other objects and features of novelty of the present invention will be specifically pointed out or will otherwise become apparent when referring, for a better understanding of the invention, to the following description taken in conjunction with the accompanying drawings, wherein:

FIGURE 1 is a side view, partly in section, of a mag netic particle clutch illustrating one embodiment of the invention;

FIG. 2 is a sectional view taken along the line 2-2 of FIG. 1 and showing by the line 11 the angle of the partial section taken for FIG. 1;

FIG. 3 is a view of the right end face of the clutch of FIG. 1;

FIG. 4 is a sectional view taken along the line 44 of FIG. 3; and

FIG. 5 is a sectional view taken along the line 5-5 of FIG. 1.

Referring now more particularly to FIGS. 1 and 4, a magnetic particle clutch embodying features of the invention is indicated generally by the reference numeral 10. It has a rotatable housing 14 with two cylindrical housing sections 16 and 18 which are mirror images of one another except for a few minor machined features. The housing sections 16 and 18 are made of a suitable magnetizable material such as a No. 5 relay steel marketed by Allegheny Ludlum, a well-known steel company.

The housing sections 16 and 18 are connected together by a plurality of bolts 24 which threadably engage the housing section 18 but extend freely through holes 26 in the housing section 16. A lock washer 28 is positioned beneath the head of each bolt 26 and engages a shoulder on the section 16 to enable the two sections to be drawn and held tightly together.

The housing sections 16 and 18 have coaxially aligned central bores 20 and enlarged outer bores 22. A shaft 30 extends through the central bores 20 and is rotatably journaled Within a pair of ball bearings 32 and 34 seated in the enlarged outer bores 22 of the sections 16 and 18, respectively. The shaft 30 is made of non-magnetizable stainless steel and is locked against axial movement by a bushing 36 bearing against the inner race of the ball bearing 34 and locked in position by a set screw 38 and a bushing 40 bearing against the inner race of the ball bearing 32 and locked in position by a set screw 42.

The right end of the shaft 30, as viewed in FIG. 1, is provided with a flat surface 44 to facilitate connection to a shaft 45 (indicated in phantom lines in FIG. 4) of a brake mechanism (not shown) for stopping rotation of the shaft 30 when the clutch is disengaged. A tight fitting sleeve 47 is slidably positioned over the joint to maintain engagement between the flat surfaces of the two shafts. The brake shaft 45 rotatably supports the right end of the shaft 30, and a ball bearing 46, illustrated in phantom in FIG. 1, may be seated on the bushing 40 to journal the left end of the shaft 30. The housing 14, in effect, provides a pulley wheel which can be rotated continuously by a pulley belt drivingly connected to a suitable prime mover, the shaft 30 rotating when the clutch is engaged and being braked to a stop by a brake mechanism when the clutch is disengaged.

An annular recess 48 is formed within each of the sections 16 and 18 in position to cooperate with one another to form an annular chamber for receiving a spool-shaped,

non-magnetizable coil bobbin 50 having a pair of concentric coils 52 and 54 wound thereabout. A high tem perature, sponge rubber washer 56 is compressed against the left end of the coil bobbin to firmly hold the coil bobbin in position. A layer 58 of a silicone rubber material is brushed onto the outer coil 54 to insulate the coils and help retain them in place.

The portions of the confronting faces of the housing sections 16 and 18 that are radially inward of the coil bobbin 50 are spaced from one another to form rotor chamber walls 60 and 62. A washer 64, made of a suitable insulating material such as polytetrafluoroethylene felt, is compressed between the chamber walls 60 and 62 to seal the outer periphery of the rotor chamber defined by the walls 60 and 62 urging the magnetic lines of flux produced by the coils to cross the rotor chamber in an axial direction.

A thin disk-shaped rotor 66 of magnetizablc material having an enlarged central hub 68 is fixed to the shaft for rotation therewith. A small clearance is provided between the washer 64 and the outer periphery of the rotor 66, and a gap is provided between the rotor 66 and each of the chamber Walls 60 and 62.

As illustrated better in FIG. 4, a double labyrinth seal 70 is formed around the hub 68 to seal the inner periphery of the rotor chamber. The seal 70 has two members 72 and 74 fixed within the bores 20 of the housing sections 16 and 18, respectively, in position to define a very small labyrinth path on each side of the rotor 66 and around the hub 68. The seal members 72 and 74 are made of a suitable non-magnetic material, such as brass, and are closed off at each end by end plates 76 and 78.

Washer-shaped spacers 80 and 82 are mounted within each of the seal members, and the space on both sides of each spacer is filled with a suitable sealing material, preferably Teflon, which slidably seals against the shaft 30. Washers 80 and 82 form annular channels 81 and 83, respectively, in which particles may collect. Thusly, leakage through the seal may be reduced. The rotor chamber is filled with magnetic powder, as will be described, and the labyrinth seal 70 very effectively seals the magnetic powder within the rotor chamber with a minimum of drag on either the rotor 66 or the shaft 30.

As most clearly illustrated in FIGS. 2 and 4, a plurality of radially extending slots 84 are formed in the outer face of each of the housing sections 16 and 18 to prevent eddy current losses. As best illustrated in FIGS. 1 and 3, a printed circuit board 86 of a suitable insulating material, such as an epoxy resin material, is attached to the center end face of the housing section .18 by a plurality of screws 88 with suitable spacers 91 to space the board 86 from the housing member 18. Three concentric conducting rings 90-94 are printed, or otherwise fixed, on the face of the board 86 in position to be slidably engaged by brushes (not shown) to supply the electrical power for energizing the coils 52 and 54, as will be described in greater detail hereinafter.

A slanted inlet orifice 96 is formed in the housing member 18 and is closed off by a pin 98 having an enlarged threaded head 100 on the end. After the clutch has been completely assembled, the rotor chamber can be filled with the magnetic powder mixture through the orifice 96, and the orifice thereafter is closed by the pin 98. To remove the powder from the rotor chamber, if this should become necessary, the pin 98 is removed and a tube inserted in the orifice for pulling the powder out by a vacuum.

A wire 102 connects the ring 90 to one end of the coil 52, a wire 104 connects the ring 92 to the other end of the coil 52 and to one end of the coil 54, and a wire 106 connects the conducting ring 94 to the other end of the coil 54. All three wires extend into one of the slots 84 to make the above-described connections.

With this arrangement, the coil 52 can be energized by a large pulse of current to the conducting rings 90 and 92 for a short duration to build up the magnetic field rapidly. Thereafter, the current is reduced andmaintained at a lower level for normal running. The electrical power is supplied, for intermittent cycling operation, in the form of pulses ranging from 0 to cycles per second.

As long as the coils 52 and 54 are deenergized, the housing 14 rotates freely upon the shaft 30. When the coil 52 is energized, the magnetic powder in the rotor chamber will be magnetized so as to be attracted to the disk-shaped rotor and to the chamber walls 60 and 62 to cause the rotor and the shaft 30 to rotate with the housing 14. The faces of the rotor may be roughened, as illustrated by the numeral 109 in FIG. 5, and a plurality of holes 110 may be provided in the rotor to improve the clutching action when the magnetic powder is magnetized.

By providing the two coils and three conducting rings 90, 92 and 94, the mixture can be deenergized more rapidly in order to obtain cycles of operation as high as 100 cycles per second. For example, after the coil 52 is energized to engage the clutch, the clutch is disengaged by turning off the current to the coil 52 and applying a current pulse to the coil 54 in the opposite direction, resulting in a more rapid collapse of the magnetic field.

The construction of the brake mechanism can be identical to that of the clutch 10 with the exception that the housing thereof would be fixed against rotation rather than continuously rotated as is the housing 14. Thus, the shaft 31 of the brake mechanism keyed to the right end of the shaft 30, as illustrated in FIG. 4, will rotate freely when the coils of the brake mechanism are deenergized and will be locked against rotation when the coils are energized.

The size of the gap between the rotor 66 and the chamber walls 60 and 62 also is very important to the high speed performance of the clutch 10. In the embodiment illustrated, the axial dimension of each gap is .008 inch, and the radial dimension of the rotor chamber is such as to require .9 gram of the specific powder mixture of the present invention to fill the rotor chamber. By making the gaps equal, .45 gram of the powder is positioned on each side of the rotor.

The exact formulation of the magnetic powder of the present invention consists of a mixture of number 410 stainless steel particles 5 to 10 microns in diameter, which particles do not oxidize readily, and a microsize Molykote lubricant for reducing the drag on the rotor when the coils are deenergized. The quantity of lubricant is one to five percent by weight of the total mixture of the magnetic particles and lubricant and preferably is three percent by weight of the total mixture. Increasing the percentage of the lubricant decreases the operating or response time of the clutch and decreasing the percentage of the lubricant increases the operating or response time, but in the latter case the magnetic particles may tend to seize or pack in a manner detrimental to the operation of the clutch. The Molykote lubricant is marketed by the Alpha-Molykote Corporation.

While it will be apparent that the embodiment of the invention herein disclosed is well calculated to fulfill the objects of the invention, it will be appreciated that the invention is susceptible to modification, variation and change without departing from the proper scope or fair meaning of the subjoined claims.

What is claimed is:

1. A high speed instrument clutch comprising:

a housing having a central bore therethrough and a washer-shaped rotor chamber therein communicating with the central bore,

a shaft extending through said central bore in spaced relation to the portion of the wall thereof adjacent,

to said rotor chamber,

bearing means for rotatably journaling said housing on said shaft,

a disk-shaped rotor fixed to said shaft with the outer portion thereof extending within said chamber,

a pair of concentric coils mounted within said housing in position to encircle the outer periphery of said rotor,

means mounted on said housing and electrically connected to said coils in a manner to enable one of said coils to be energized independently of the other,

seal means mounted within said bore for preventing magnetic particles escaping from said rotor chamber including a seal housing fixed within said bore on each side of said rotor,

the inner ends of said seal housings cooperating with said rotor to provide a double labyrinth path on each side of the rotor, and

sealing material Within each of said seal housings slidably sealing against said shaft outwardly of said labyrinth paths.

2. A high speed instrument clutch comprising:

a housing having a central bore therethrough and a washer-shaped rotor chamber therein communicating with the central bore, said housing comprising two housing sections which are mirror images of one another, and means for connecting said members together,

a plurality of circumferentially spaced radially eX- tending slots formed in each of said housing sections in a manner to reduce eddy currents,

a shaft extending through said central bore in spaced relation to the portion of the wall thereof adjacent to said rotor chamber,

bearing means for rotatably journaling said housing on said shaft,

a disk-shaped rotor fixed to said shaft with the outer portion thereof extending within said chamber, coil means mounted in said housing for producing a magnetic field across said chamber in an axial direction,

seal means mounted within said bore for preventing magnetic particles escaping from said rotor chamber including a seal housing fixed within said bore on each side of said rotor,

the inner ends of said seal housings cooperating with said rotor to provide a double labyrinth path on each side of the rotor, and

sealing material within each of said seal housings slidably sealing against said shaft outwardly of said labyrinth paths.

3. A high speed instrument clutch comprising:

a housing having a central bore therethrough and a washer-shaped rotor chamber therein communicating with the central bore,

a shaft extending through said central bore in spaced relation to the portion of the wall thereof adjacent to said rotor chamber,

bearing means for rotatably journaling said housing on said shaft,

a disk-shaped rotor fixed to said shaft with the outer portion thereof extending within said chamber,

coil means mounted in said housing for producing a magnetic field across said chamber in an axial direction,

a powder-like mixture filling said rotor chamber comprising magnetic particles made of number 410 stainless steel ranging from 5 to 10 microns in diameter and mixed with a microsize Molykote lubricant, said lubricant comprising one to five percent by weight of the total mixture,

seal means mounted within said bore for preventing magnetic particles escaping from said rotor chamber including a seal housing fixed within said bore on each side of said rotor,

the inner ends of said seal housings cooperating with said rotor to provide a double labyrinth path on each side of the rotor, and

sealing material within each of said seal housings slidably sealing against said shaft outwardly of said labyrinth paths.

4. The invention as defined in claim 3 wherein the rotor chamber walls closely overlie each face of the rotor to form gaps between the rotor faces and the chamber walls, each of said gaps having an axial dimension of substantially .008 inch whereby the same quantity of magnetic particles can be positioned adjacent to each face of said rotor.

References Cited UNITED STATES PATENTS 2,650,684 9/1953 English et al. 19221.5 2,671,545 3/1954 Petrofi? 19221.5 2,804,955 9/1957 Gill 19221.5 2,809,732 10/1957 Logan et al. 192-215 2,885,044 5/1959 Jaeschke 192-21.5 2,897,931 8/1959 Didszuns 19221.5 3,026,978 3/1962 Carrard 19221.5 X 3,216,542 11/1965 Comstock 19221.5

OTHER REFERENCES Electrical Manufacturing Publication, vol. 63, February 1959, p. 11.

MILTON KAUFMAN, Primary Examiner.

DAVID J. WILLIAMOWSKY, FRED C. MATTERN, Examiners,

C. J. HUSAR, Assistant Examiner, 

1. A HIGH SPEED INSTRUMENT CLUTCH COMPRISING: A HOUSING HAVING A CENTRAL BORE THERETHROUGH AND A WASHER-SHAPED ROTOR CHAMBER THEREIN COMMUNICATING WITH THE CENTRAL BORE, A SHAFT EXTENDING THROUGH SAID CENTRAL BORE IN SPACED RELATION TO THE PORTION OF THE WALL THEREOF ADJACENT TO SAID ROTOR CHAMBER, BEARING MEANS FOR ROTATABLY JOURNALING SAID HOUSING ON SAID SHAFT, A DISK-SHAPED ROTOR FIXED TO SAID SHAFT WITH THE OUTER PORTION THEREOF EXTENDING WITHIN SAID CHAMBER, A PAIR OF CONCENTRIC COILS MOUNTED WITHIN SAID HOUSING IN POSITION TO ENCIRCLE THE OUTER PERIPHERY OF SAID ROTOR, MEANS MOUNTED ON SAID HOUSING AND ELECTRICALLY CONNECTED TO SAID COILS IN A MANNER TO ENABLE ONE OF SAID COILS TO BE ENERGIZED INDEPENDENTLY OF THE OTHER, SEAL MEANS MOUNTED WITHIN SAID BORE FOR PREVENTING MAGNETIC PARTICLES ESCAPING FROM SAID ROTOR CHAMBER INCLUDING A SEAL, HOUSING FIXED WITHIN SAID BORE ON EACH SIDE OF SAID ROTOR THE INNER ENDS OF SAID SEAL HOUSINGS COOPERATING WITH SAID ROTOR TO PROVIDE A DOUBLE LABYRINTH PATH ON EACH SIDE OF THE ROTOR, AND SEALING MATERIAL WITHIN EACH OF SAID SEAL HOUSINGS SLIDABLY SEALING AGAINST SAID SHAFT OUTWARDLY OF SAID LABYRINTH PATHS. 